The present invention relates to a switch for use with various input devices in a personal computer and a word processor, for example, and more particularly to a switch of a type such that a terminal of a fixed contact member and a terminal of a movable contact member in the switch are projected from a lower surface of a case body, and they are soldered to a soldering land of a printed circuit board.
FIGS. 2 to 5 show a prior art push button switch, wherein FIG. 2 is a vertical sectional view of the push button switch; FIG. 3 is a bottom plan view of the push button switch with its lower case removed; FIG. 4 is an exploded perspective view of a switch element to be installed in the push button switch; and FIG. 5 is a vertical sectional view of the push button switch mounted on the printed circuit board.
Referring to FIGS. 2 and 3, a lower case 1 and an upper case 2 are assembled with each other by snap coupling means (not shown). The upper case 2 is formed at its upper central position with an insert hole 2a for inserting therethrough a stem 3 constituting a part of an operating member. A spring 5 is interposed between the stem 3 and a bottom inner surface of the lower case 1. A key top 4 as the operating member is fixedly engaged with an upper portion of the stem 3.
A switch element 6 is installed at a side portion of an inner space defined by the lower case 1 and the upper case 2. As shown in FIG. 3, the switch element 6 is supported to the upper case 2 in such a manner as to be prevented from moving toward the stem 3 by a pair of inward projections 2b of the upper case 2. A pusher spring 11 is fixedly engaged with an upper portion of the switch element 6. The pusher spring 11 has a bent portion 11a, an elongated portion 11b, and an operating projection 11c. The elongated portion 11b extends to a lower side of the stem 3, and is formed at its lower end with a forked portion adapted to enter a reciprocating area of the stem 3.
A leaf spring 12 is provided in the inner space of the case body on the opposite side of the switch element 6 with respect to the stem 3. The leaf spring 12 has an upright portion 12a extending along a side wall surface of the upper case 2 and an elongated portion 12b extending to the lower end of the stem 3. A lower end of the elongated portion 12b constitutes a click projection 12c abutting against the lower portion of the stem 3 and adapted to retractably enter the reciprocating area of the stem 3. The upright portion 12a is sandwiched between the side wall of the upper case 2 and a retainer plate 13. The retainer plate 13 is supported to the upper case 2 in such a manner as to be prevented from moving toward the stem 3 by a pair of inward projections 2c of the upper case 2.
As shown in FIG. 4, the switch element 6 consists of an operating member 7 formed of synthetic resin, a movable contact member 8 formed of metal, a spacer 9 formed of synthetic resin, and a fixed contact member 10 formed of metal. The operating member 7 is formed with a pushing portion 7a. The movable contact member 8 consists of a frame 8a, a metal thin plate 8b supported to the frame 8a and a terminal 8d extending downwardly from the frame 8a. The spacer 9 is formed with a circular central opening 9a. The fixed contact member 10 has a fixed contact 10a exposed through the opening 9a of the spacer 9 to the metal thin plate 8b of the movable contact member 8 and also has a terminal 10c extending downwardly from a lower end of the fixed contact member 10. The movable contact member 8, the spacer 9 and the fixed contact member 10 are formed at their peripheral portions with through-holes 8c, 9b and 10b, respectively, which are arranged coaxially. The operating member 7 is formed at its rear surface with a pair of projections (not shown) to be inserted through the through-holes 8c, 9b and 10b and be caulked at their ends. Thus the components of the switch element 6, that is, the operating member 7, the movable contact member 8, the spacer 9 and the fixed contact member 10 are laminated together.
In operation, when the key top 4 is in an undepressed position as shown in FIG. 2, the stem 3 is disposed at an uppermost position in receipt of a return biasing force of the spring 5 and return biasing forces of the pusher spring 11 and the leaf spring 12. Under the condition, this operating projection 11c of the pusher spring 11 does not push the pushing portion 7a of the operating member 7, resulting in separation of the metal thin plate 8b of the movable contact member 8 from the fixed contact 10a of the fixed contact member 10. Thus, the switch is maintained in an off state.
When the key top 4 is depressed, the stem 3 is lowered against the biasing force of the spring 5 to retract the click projection 12c of the leaf spring 12 from the reciprocation area of the stem 3 and thereby providing 9 click feeling. At the same time, the pusher spring 11 is also retracted from the reciprocation area of the stem 3 by the lowering motion of the stem 3. As a result, the pushing portion 7a of the operating member 7 is pushed by the operating projection 11c of the pusher spring 11 to displace the metal thin plate 8b of the movable contact member 8 so as to bring the same into contact with the fixed contact 10a of the fixed contact member 10. Thus, the switch is turned on.
When the depression force applied to the key top 4 is removed, the stem 3 is returned to the uppermost position as shown in FIG. 2. Accordingly, the pushing force of the operating projection 11c against the pushing portion 7a is removed to thereby cause the metal thin plate 8b to separate from the fixed contact 10a. Thus, the switch is turned off again.
As shown in FIG. 5, the push button switch as mentioned above is mounted on a printed circuit board 14 by soldering the terminal 8d of the movable contact member 8 and the terminal 10c of the fixed contact member 10 projecting from the lower case 1, to the soldering lands 14a of the printed circuit board 14 by auto-dipping. In soldering the terminals 8d and 10c to the soldering lands 14a, a flux is applied to the soldering lands 14a and the terminals 8d and 10c for the purpose of improving the solderability. However, since the flux has a good wettability to a metal surface, it tends to enter the inside of the lower case 1 along the surfaces of the terminals 8d and 10c. Then, the flux is moved to the switch element of a laminated structure, namely, the frame 8a or the fixed contact member 10 contacting the bottom inner surface of the lower case 1, and is finally deposited onto the metal thin plate (movable contact) 8b or the fixed contact 10a. As the flux is an electrically insulating material, the deposition of the flux to the contact portion causes imperfect electrical contact.
To prevent the entry of the flux to the contact portion, an adhesive is applied to a gap between the lower case 1 and the terminals 8d and 10c. However, the additional step of applying the adhesive causes an increase in cost.